The invention is based on a fuel injection pump for internal combustion engines as defined hereinafter. In a fuel injection pump of this type known from German Patent 33 14 360, a pump piston is moved axially back and forth in a cylinder bore by a cam drive with its end remote from the cam drive, the pump piston defines a pump work chamber in the cylinder bore of a cylinder liner that can be supplied with fuel during a portion of the pump piston stroke via a radial control opening in the cylinder liner. The pump piston is rotatable via a governor rod and on its jacket face has an oblique control edge, communicating with the pump work chamber via a longitudinal groove, and with this control edge it cooperates with the radial control opening of the cylinder liner for the sake of varying the fuel injection quantity.
The contour of the control opening is embodied such that during the diversion process, a maximally large opening cross section is made available rapidly, so that the pump work chamber and an injection valve, connected to it via an injection line and protruding into the combustion chamber of the engine to be supplied, is pressure-relieved as fast as possible, which results in a fast closure of the injection valve. To that end, the control opening is in the shape of an egg, flattened on one long side; this flattened side is oriented toward the oblique control edge of the pump piston and cooperates with it during the diversion process. In the known fuel injection pump, however, the disadvantage arises that because of the embodiment of the upper end of the control opening as a circular arc with a very large radius, which is closed at the onset of fuel injection by the end of the pump piston remote from the cam drive, a very rapid pressure rise in the pump work chamber takes place. The result is even at the onset of combustion in the combustion chamber, a large fuel quantity is injected, which combusts abruptly and thus leads to severe strain on the component and is very noisy. Accordingly, with the known fuel injection pump it is not possible to adapt both the beginning and the end of high-pressure pumping in the pump work chamber optimally to the conditions of the engine to be supplied.